Pearson: Fishes of the Rio Beni Basin 
37 
distinct, not extended on the middle caudal rays; a silvery 
lateral band ; back and sides with many chromatophores ; pec- 
torals, ventrals, anal, and caudal fins unmarked. 
Subfamily tetragonopterin^e. 
Tetragonop terns argenteus Cuvier. 
17185, 5, 25-40 mm., Cachuela Esperanza. Mar., 1922. 
17186, 1, 75 mm., Ixiamas. Dec., 1921. 
The above specimens have 40 and 41 rays in the anal. 
Mcenkhausia sanctae filomenae (Steindachner) . 
17197, 8, 52-80 mm., Ixiamas. Dec., 1921. 
17198, 4, 35-45 mm., Lagoons, Lake Rogoagua. Nov., 1921. 
17199, 1, 40 mm., Lagoon near Reyes. Oct., 1921. 
The above specimens are intermediate between M. oligolepis 
and M. sanctse filomenx. Anal and lateral line counts follow : 
anal rays 
lateral line 
25 
26 
27 
28 
29 
22 
23 
24 
25 
26 
27 
28 
Ixiamas 
1 
2 
3 
2 
1 
1 
3 
3 
Lagoons, Lake Rogoagua 
1 
1 
1 
1 
1 
2 
1 
Lagoons, near Reyes . . 
1 
1 
Mcenkhausia dichroura (Kner) . 
17189, 116, 55-66 mm., Rurrenabaque. Oct., 1921. 
17190, 2, 73 and 85 mm., Lake Rogoagua. Nov., 1921. 
17191, 1, 45 mm., Cachuela Esperanza. Mar., 1922. 
17192, 10, 60-66 mm., Popoi River, Upper Beni. Sept., 1921. 
Mcenkhausia intermedia Eigenmann. 
17193, 28, 24-40 mm., Lagoon near Reyes. Oct., 1921. 
17194, 24, 30-40 mm., Beni system, locality unknown. 
17195, 7, 25-32 mm., Ivon. Feb., 1922. 
17196, 14, 35-45 mm., Lagoons, Lake Rogoagua. Nov., 1921. 
Mcenkhausia intermedia is a good species. It differs from 
M. dichroura by possessing a narrow maxillary with a straight 
border. The maxillary of M. dichroura has an arched border 
and is wider than that of M. intermedia. Anal and scale 
counts of specimens of Mcenkhausia dichroura taken at ran- 
dom follow: 
